Firth, Flood, Flood Current, Floodmark, Flood Tidal Delta: Word Origins, Descriptions of Coastal Features, Processes

In the current alphabetic series of word origins and physical descriptions of coastal features and processes, here are firth, flood, flood current, flood interval, floodmark, flood strength, flood tidal delta, and flood tide.

Firth
Modern English firth comes from Middle English firth, from Old Norse fjorthr. The word is akin to Old English ford ("ford"), Old English faran ("to go"), and Latin portus ("port").

A firth is a narrow arm of a sea, especially an opening between a sea and a river, that is, an estuary. An archaic form of the word is frith.

The word is most familiar as part of place-names in northern England and Scotland. A famous example is the Firth of Forth, an estuary in Scotland between the River Forth and the North Sea.

Flood
Modern English flood comes from Middle English flood, from Old English flod. The word is akin to Old High German fluot ("flood") and Old English flouan ("to flow").

The word flood is used in at least three different senses in tidal terminology: the flowing in, that is, the rising current, of a tide; the period during which the tide level is rising; and the highest point of a tide.

Another coastal use of flood refers to a flow above the normal capacity of a channel or other waterway.

Flood Current
A flood current is a tidal current that moves toward a shore or up a tidal river.

Flood Interval
The interval between the passing of the moon over the meridian of a specific location and the time of the following tide at that place is known as the flood interval.

Floodmark
A floodmark is a mark or line on a shore indicating the highest point to which the tide, or flood, rises. Also known as a high-water mark.

Flood Strength
A flood current at its greatest velocity is called a flood strength.

Flood Tidal Delta
A delta is an alluvial deposit at the mouth of a river. The name refers to the typical triangular shape of the deposit (delta is the name of the fourth letter of the Greek alphabet, which, in its capital form, looks like a triangle).

Similarly, a ridge of sand deposited by tidal currents at the mouth of a tidal inlet is called a flood tidal delta.

Flood Tide
The term flood tide has at least three different coastal meanings: a rising tide or flood current; the period between the minimum height of a falling tide and the maximum height of the following rising tide; and a tide at its greatest height.
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Encyclopaedia Britannica Ready Reference 2004. CD-ROM. Encyclopaedia Britannica, 2004.

Merriam-Webster's Collegiate Dictionary. 11th ed. Springfield, Mass.: Merriam-Webster, 2006.

Merriam-Webster's Geographical Dictionary. 3rd ed. Springfield, Mass.: Merriam-Webster, 2007.

The Oxford English Dictionary. 2nd ed. Oxford, England: Clarendon Press, 1989.